A quantitative gas chromatographic determination of ethosuximide based on N-butylation

A gas chromatographic procedure has been developed for the routine determination of the anticonvulsant, ethosuximide, in serum. Volatile butyl derivatives for gas chromatography were prepared by the method of R.H. Greeley (J. Chromatogr., 88 (1974) 229) using butyl iodide as the alkylating agent. This procedure yielded stable derivatives with improved chromatographic qualities over those obtained by methylation and proved superior to both on-column alkylation with tetrabutylammonium hydroxide and to silylation. The analysis requires 0.5 ml of serum and the between run precision of the assay at 40 mug/ml was 3.3%.